نشریه آنالیز سازه - زلزله
سال نوزدهم شماره 1 (بهار 1401)

Today, the reinforcing polymer composites are widely applied to improve the seismic behavior of the structures. The history of structures reinforced with polymer sheets is mostly related to the reinforcement of beams and columns. In this study, the behavior coefficient of a special concrete moment-resisting frame in combination with a concrete shear wall (CSW) with opening and retrofitted with Carbon fiber reinforced polymer (CFRP) was calculated.  The CSW was added as a reinforcement to the pre-designed concrete moment-resisting frame at two heights of 8 and 12 floors, then circular, rhombic and rectangular openings were created in the walls and CFRP were added around the openings along 45 and 90 degrees on one side and both sides of the wall. The results of the analyses presented that the strength of the structure decreased with the opening of the wall, and when the fibers were added around the opening, the resistance increased slightly; this slight increase in strength is due to the low amount of fibers. To cope with this issue, a layer of fibers was glued to the wall area on one side, on both sides, and two layers of fibers on one side of the wall around the opening. The interpretation of the results indicated that the higher the level of reinforcing fibers on the wall, the higher the capacity and behavior coefficient of the structure. The addition of CFRP on both sides of the wall had a better effect on the behavior coefficient and capacity of the structure than the application of two layers of fibers on one side of the wall.

Retrofitting of buildings and improving their performance has received a lot of attention from researchers and engineers in recent years. With the advancement of technology and the presentation of new materials in the field of construction, the quality of retrofitting and improving of structures has also enhanced. Many structures in the world have been built using reinforced concrete materials, which have exhibited a good performance during previous earthquakes, too. The reinforcement of these structures and the presentation of new solutions to improve their performance have also been studied by many researchers and various solutions such as the use of concrete jackets have been proposed and applied. In the present study, using the posttensioned concrete, a new approach is presented to strengthen the flexural strength of reinforced concrete beams using ABAQUS software. In this method, by adding a posttensioned concrete layer to the reinforced concrete beam (base sample) from both sides, its flexural performance has been investigated. The results of the analyses indicate the appropriate behavioural compatibility of this method due to the high tensile capacity of steel cable, which can have a significant effect on ductility, improving  performance, increasing the capacity of reinforced concrete beams and transferring of the plastic joint from the middle span to  of the end of the beam.

The first steel shear walls were mainly utilized in retrofitted form, but steel shear walls are now known to offer reliable performance without stiffeners. With low thickness and yield strength, the plate would buckle under small loads, transitioning from an in-plane shear mechanism to the diagonal tension field. Using ABAQUS, the present study takes a numerical approach and investigates a three-story, single span Reinforced Concrete Frame (RCF) with Low Yield Point (LYP) steel infill plates. A total of 45 models were studied. The yield stress of the shear wall, shear wall thickness, and the span-to-height ratio of the RCF were evaluated for the RCF, and the numerical models were compared in terms of secant stiffness, yield load, maximum load, yield displacement, and dissipated energy. Changing the span-to-height ratio and the thickness and yield strength of the LYP steel plate, increased the secant stiffness by, respectively, 49.39, 45.59, and 59.67%, the ultimate strength by 27.64, 30.88, and 40.73%, and energy dissipation by 32.35, 34.19, and 44.9%. The failure modes in the numerical models of RCFs with LYP steel plate shear walls resulted from local buckling and wrinkling of the steel infill plate. The yield strength of the LYP steel plate was found to control the stiffness, flexural strength, and energy dissipation in the RCF with a steel plate shear wall. Moreover, longitudinal cracks were created in the concrete in columns and beams due to the transfer of momentum by the tension field of the steel infill plates.

TADAS additional dampers are a type of passive control system that can be used in seismic design or retrofitting of offshore structures. The most common type of fixed offshore structures that are used include jacket or template platforms. These dampers in combination with offshore structures through the consumption of a large part of the input energy of the earthquake, greatly reduce the demand for energy loss by the main members of the frame in this type of structures and therefore increase the safety of structures. In the present study, the behavior of TADAS dampers in large displacements in SPD21 platform, which is one of the offshore platforms of South Pars phase 1, was investigated and some possible incorrect details in its design, which if not paid attention can cause damage to the structure, were reviewed and analyzed. To investigate this issue, the TADAS damper was simulated in full detail in the SPD21 offshore structure in ABAQUS finite element software and was subjected to continuous earthquake loading resulting in the large displacements. It was found out that the stiffness of the damper increases sharply and abruptly in a large displacement, which can lead to undesirable responses and even help to destroy the marine structure, and the looseness of the pins delays damper performance and increases the likelihood that dampers will play a lesser role in the earthquakes. In this research, it was deduced that if the height of the TADAS damper gap is increased up to 9 cm and the pins are at the lowest point inside the gap when installing the damper, the TADAS dampers installed on the template platform will be able to withstand the forces of earthquake and large displacements caused by them up to 17.9 cm which will play an important role in the stability of template platform structures such as SPD21 in the event of an earthquake and large displacements.

To improve the behavior of seismic system and increasing the capacity of structures, using of dampers is a suitable method for energy dissipation and reduction of seismic demand. The behavior of structures during earthquake has a direct relationship with the stiffness, ductility and hysteresis curves of the energy dissipation of the resistant system. Controlling and dissipating the energy input to the structure in order to reduce earthquake damage is a perfect way to meet the needs of structures. For this purpose, a system has been introduced that is utilized as a fuse during the earthquake due to its high ductility and prevents damage to the main elements of the structure. In this study, a specific type of yield damper with torsional behavior named yield-torsional damper or TFD is investigated and the energy absorption capacity of the structure is evaluated. It was observed that this system increases the power of structural energy absorption. For this purpose, the proposed system has been numerically examined nonlinearly in ABAQUS software. The results of this research indicate that the application of TFD dampers results in the structure to depreciate energy in the interface member and significantly reduces the contribution of other structural members in the energy absorption and puts the behavior of the structure at a better performance level.

In this research, the strengths and weaknesses of lateral systems of tall buildings are identified and a suitable system is proposed both technically and economically. In this regard, for a hypothetical 45-storey building, three types of pipe in pipe system with truss belt cap, moment frame system with truss belt cap and central core system with restraint arm and truss belt are compared. Nonlinear analysis of the structure was performed by pushover method. In addition, the relative displacement of the floors was extracted by ETABS software. The results revealed that the central core system with the restraint arm and truss belt in a hypothetical 45-storey building is economically more viable than other systems. Another consequence is that the closer the truss belt is to the ground floors, the better the performance of the structural system. Although this makes the bracing sections heavier, it will not have much effect on the overall weight of the structure.